The overall objective of this project is to extend our knowledge of the processes by which the listener analyzes the speech signal in order to derive the linguistic message. Specifically, we are proposing two lines of research to investigate the tuning properties of the feature detectors, or perceptual channels, that underlie the analysis of phonetic feature information. All of our research will be conducted with adult human subjects. Our experiments on selective tuning will derive the output functions for detectors underlying the analysis of three phonetic features, voicing, place of articulation, and manner of articulation. We will approach this problem in two ways: In one set of experiments we will estimate output functions by determining the extent to which the relative effectiveness of a stimulus in dichotic competition varies as a function of the acoustic value of the stimulus. In the other set of studies we will measure the magnitude of adaptation as a function of the acoustic value of the adapting stimulus and use the degree to which a stimulus is an effective adaptor as a measure of the extent to which it activated the detector. Our experiments on context-dependency are aimed at determining the extent to which channels for voicing, place, and manner analysis are tuned to information specifying phonetic context. We will investigate the dependency patterns among these three features and we will determine the degree to which the dependencies operate in terms of the acoustic or phonetic value of the contextual information. These experiments will employ a selective adaptation procedure in which we vary the value of the adapting stimulus along a contextual dimension. The extent to which this variation results in a decrement in adaptation will be taken as an estimate of context-dependency.